1. Field of the Invention
The present invention relates to a dual-mass flywheel. More specifically, the present invention relates to a dual-mass flywheel whereby a second flywheel is elastically connected in the rotation direction with a member on the crankshaft side.
2. Background Information
Conventionally, a flywheel is attached to a crankshaft of an engine to absorb vibrations caused by variations in engine combustion. Further, a clutch device is arranged on a transmission side (i.e., in a position axially shifted toward the transmission) with respect to the flywheel. The clutch device usually includes a clutch disk assembly coupled to an input shaft of the transmission, and a clutch cover assembly to bias the frictional coupling portion of the clutch disk assembly toward the flywheel. The clutch disk assembly typically has a damper mechanism for absorbing and damping torsional vibrations. The damper mechanism has elastic members such as coil springs arranged to compress in a rotating direction.
A structure is also known in which the damper mechanism is not arranged in the clutch disk assembly, and rather is arranged between the flywheel and the crankshaft. Specifically, the flywheel is divided into two major components such that a first flywheel is fixed to the crankshaft, and a second flywheel is connected to the crankshaft or to the first flywheel via the damper mechanism. In this structure, the flywheel is located on the output side of a vibrating system, in which the coil springs form a border between the output and input sides, so that inertia on the output side is larger than that in other prior art. Consequently, the resonance rotation speed can be lower than an idling rotation speed so that damping performance is improved. The structure, in which the flywheel and the damper mechanism are combined as described above, provides a flywheel assembly or a flywheel damper. Japanese Laid-open Patent Application No. 10-231897 shows an example of one such flywheel.
In the conventional dual-mass flywheel, the second flywheel is supported to be able to rotate via a bearing with respect to a member on the crankshaft side. The term “member on the crankshaft side” used herein refers to the crankshaft, the first flywheel, and any member fixed to the first flywheel or to the crankshaft.
A ball bearing or bushing, for example, is used as the bearing. The ball bearing is usually composed of an inner race, an outer race, and a plurality of balls. The bushing is made of a cylindrical standalone member.
A ball bearing, as such, has drawbacks in that it has a relatively high cost and that its large radial dimension occupies a relatively large amount of space. A ball bearing also inherently has low rigidity in the bending direction of the axle, and is therefore unable to create adequate resistance to bending vibrations when a dual-mass flywheel is used. In other words, the members that are supported by the ball bearing can easily move around and/or on the ball bearing in the axial direction.
A bushing has low wear resistance and the clearance thereof is difficult to manage, so the gap between the bushing and the peripheral surfaces of the first and second flywheels can easily become unnecessarily large.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved a dual-mass flywheel. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.